JP7005969B2 - Tire mold - Google Patents

Description

The present invention relates to a mold for manufacturing a tire.

In the tire vulcanization step, the low cover is heated while being pressurized in a cavity surrounded by a mold and a bladder or a rigid core. By pressurization and heating, the rubber composition of the low cover flows in the cavity. At this time, if air remains between the cavity surface of the mold and the low cover, a bear is formed on the surface of the tire. There is a demand for a mold in which this residual air is prevented.

There are molds with multiple pieces to prevent air retention. In the vulcanization process, the inner surface of this piece comes into contact with the tread surface of the low cover. In this mold, by arranging the pieces, a cavity surface for forming a tread surface is formed. A gap (referred to here as a slit) is provided between pieces adjacent to each other. The air between the low cover and the cavity surface moves to this slit and is discharged from this slit. A study on a mold including a plurality of pieces is disclosed in Japanese Patent Application Laid-Open No. 2011-116020.

Japanese Unexamined Patent Publication No. 2011-116020

As the mold is used in the manufacture of tires, the width of the slits can fluctuate. If the slit width is small, air discharge may be hindered. The mold is required to suppress the generation of bears due to this deterioration in exhaust performance. Further, when the slit width becomes large, the rubber composition easily enters the slit. The mold is required to suppress the generation of burrs due to the rubber composition entering the slit.

An object of the present invention is to provide a mold for a tire in which the generation of bears and the generation of burrs are suppressed.

The mold according to the present invention includes a plurality of pieces. By arranging the above pieces, a cavity surface for forming a tread surface of the tire is formed. A slit is provided between the pieces adjacent to each other. The cavity surface comprises an exhaust groove extending along the boundary of the pieces adjacent to each other. The opening of the slit is located on the inner surface of the exhaust groove.

Preferably, the width of the exhaust groove is 0.05 mm or more and 0.5 mm or less.

Preferably, the contour of the cross section of the exhaust groove is rectangular or arcuate.

Preferably, the cavity surface further comprises sub-exhaust grooves extending in contact with or intersecting the plurality of exhaust grooves.

Preferably, the boundaries of the adjacent pieces are curved.

The method for manufacturing a tire according to the present invention is
The process of obtaining a low cover,
And a plurality of pieces, a cavity surface for forming a tread surface of a tire is formed by arranging these pieces, a slit is provided between the pieces adjacent to each other, and the cavity surfaces are adjacent to each other. The low cover is vulcanized in a mold having an exhaust groove extending along the piece and having an opening of the slit located on the inner surface of the exhaust groove.

In the tire mold according to the present invention, the opening of the slit is located on the inner surface of the exhaust groove. Even if the slit width becomes smaller, air is discharged through the exhaust groove. In this mold, the deterioration of the exhaust performance is suppressed. In this mold, the generation of bears is suppressed. This exhaust groove relieves the pressure with which the rubber composition enters the slit. In this mold, even if the slit width is increased, the rubber composition is suppressed from entering the slit. In this mold, the generation of burrs is suppressed.

FIG. 1 is a plan view showing a part of a tire mold according to an embodiment of the present invention. FIG. 2 is a cross-sectional view taken along the line II-II of FIG. FIG. 3 is a cross-sectional view showing the segments of the mold of FIG. FIG. 4 is a view of the segment of FIG. 3 as viewed from the inside in the radial direction. FIG. 5 is an enlarged view of a part of the cavity surface of the segment of FIG. FIG. 6 is a cross-sectional view taken along the line VI-VI of FIG. FIG. 7 is an enlarged cross-sectional view of the tire mold according to another embodiment of the present invention in the vicinity of the boundary of the pieces. FIG. 8 is a view of a segment of a tire mold according to still another embodiment of the present invention as viewed from the inside in the radial direction. FIG. 9 is an enlarged view of a part of the cavity surface of the segment of FIG. FIG. 10 is a cross-sectional view taken along the line XX of FIG.

Hereinafter, the present invention will be described in detail based on a preferred embodiment with reference to the drawings as appropriate.

FIG. 1 shows a tire mold 2. In FIG. 1, the direction perpendicular to the paper surface is the axial direction, and the direction indicated by the double-headed arrow A is the circumferential direction. FIG. 2 is a cross-sectional view taken along the line II-II of FIG. In FIG. 2, the direction indicated by the arrow X is the radial direction, the direction indicated by the arrow Y is the axial direction, and the direction perpendicular to the paper surface is the circumferential direction. FIG. 2 also shows a low cover R (unvulcanized tire).

The mold 2 includes a large number of segments 4, a pair of side plates 6, and a pair of bead rings 8. The planar shape of the segment 4 is substantially arcuate. A large number of segments 4 are arranged in a ring shape. The number of segments 4 is usually 3 or more and 20 or less. The side plate 6 and the bead ring 8 are substantially ring-shaped.

FIG. 3 is a cross-sectional view showing segment 4 of the mold 2 of FIG. In FIG. 3, the direction indicated by the arrow X is the radial direction, the direction indicated by the arrow Y is the axial direction, and the direction perpendicular to the paper surface is the circumferential direction. As shown in FIG. 3, the segment 4 includes a holder 10 and a piece 12. The piece 12 is attached to the holder 10. The piece 12 is fitted inside the holder 10 in the radial direction. Typically, the holder 10 is made of steel or an aluminum alloy. Typically, the piece 12 is made of steel or an aluminum alloy.

FIG. 4 is a view of the segment 4 as viewed from the inside in the radial direction. Only piece 12 of segment 4 is shown in this figure. In FIG. 4, the direction indicated by the double-headed arrow A is the circumferential direction, the direction indicated by the arrow Y is the axial direction, and the direction perpendicular to the paper surface is the radial direction. The cross section of the piece 12 of FIG. 3 described above is a cross section along the line III-III of FIG.

As shown in FIG. 4, the segment 4 includes a plurality of pieces 12. In this embodiment, each piece 12 extends approximately axially. These pieces 12 are arranged in parallel in the circumferential direction. As shown in FIG. 4, the boundaries of adjacent pieces 12 are curved. That is, the surfaces on both sides of each piece 12 in the circumferential direction are curved. The shape of this curve is the same on the opposing surfaces of the pieces 12 adjacent to each other.

In the vulcanization step, the inner surface 14 of each piece 12 comes into contact with the tread surface of the low cover R. The inner surface 14 of the piece 12 forms a part of the cavity surface 16. In this mold 2, the cavity surface 16 for forming the tread surface is formed by arranging the pieces 12. A plurality of ridges 18 are provided on the inner surface 14 of the piece 12. That is, a plurality of ridges 18 are provided on the cavity surface 16. These ridges 18 carve grooves on the tread surface. These ridges 18 form a tread pattern.

FIG. 5 is an enlarged view of the area M surrounded by the dotted line in FIG. FIG. 6 is a cross-sectional view taken along the line VI-VI of FIG. This is a view cut perpendicular to the direction in which the boundary of the piece 12 extends. In FIG. 6, the upper surface of the paper surface is the cavity surface 16. As shown in FIGS. 5 and 6, a gap (referred to as a slit 20) is provided between the pieces 12 adjacent to each other. The slit 20 extends substantially the same width.

As shown in FIG. 4-6, the cavity surface 16 is provided with an exhaust groove 22. As shown in FIG. 4, the exhaust groove 22 extends along the boundaries of pieces 12 adjacent to each other. The exhaust groove 22 extends from one end of the piece 12 to the other end. As shown in FIG. 6, the contour of the cross section of the exhaust groove 22 is arcuate.

As shown in the figure, the opening 24 of the slit 20 is located on the inner surface of the exhaust groove 22. That is, as shown in FIG. 5, when the cavity surface 16 is viewed from the inside in the radial direction, the exhaust groove 22 and the opening 24 of the slit 20 overlap each other. The exhaust groove 22 and the opening 24 of the slit 20 overlap and extend. The width of the exhaust groove 22 is larger than the width of the slit 20 having an opening inside the exhaust groove 22.

The boundaries of the segments 4 adjacent to each other (see FIG. 1) are referred to as split positions 26. Although not shown, gaps are also provided between the segments 4 adjacent to each other. That is, there is a slit 20 between the piece 12 located at the end of one segment 4 adjacent to each other on the split position 26 side and the piece 12 located at the end of the other segment 4 on the split position 26 side. It is provided. The cavity surface 16 includes an exhaust groove 22 extending along the boundary (split position 26) of these pieces 12. The opening 24 of the slit 20 between these pieces 12 is exposed on the bottom surface of the exhaust groove 22.

In the embodiment of FIG. 4, in one segment 4, pieces 12 extending substantially in the axial direction are arranged in a row in the circumferential direction. Although not shown, in one segment, two or more rows of pieces arranged in the circumferential direction may be arranged in an axial direction. When two or more rows of pieces are arranged in the axial direction, a slit is provided between the pieces adjacent to each other in the axial direction. The cavity surface is provided with an exhaust groove extending along the boundaries of these pieces. The opening of this slit is located on the inner surface of this exhaust groove.

Although not shown, pieces extending in the circumferential direction may be arranged in a row in the axial direction in one segment. At this time, a slit is provided between the pieces adjacent in the axial direction. The cavity surface is provided with an exhaust groove extending along the boundaries of these pieces. The opening of this slit is located on the inner surface of this exhaust groove. Further, in one segment, the rows of pieces arranged in the axial direction may be arranged in two or more stages in the circumferential direction. At this time, a slit is provided between the pieces adjacent to each other in the circumferential direction. The cavity surface is provided with an exhaust groove extending along the boundaries of these pieces. The opening of this slit is located on the inner surface of this exhaust groove.

The method for manufacturing a tire using the mold 2 includes a step of obtaining a low cover and a step of vulcanizing the low cover. In the process of obtaining the low cover, tire components such as carcass, belt, and tread are laminated on the outer surface of the drum of the former. As a result, the low cover R is obtained. In the step of vulcanizing the low cover, the low cover R is charged into the mold 2. The low cover R is pressed against the cavity surface 16 of the mold 2 by a bladder and is pressurized. At the same time, the low cover R is heated. The rubber composition flows by pressurization and heating. The rubber undergoes a cross-linking reaction when heated. That is, in this mold 2, the low cover R is vulcanized to obtain a tire. A rigid core may be used instead of the bladder.

Hereinafter, the action and effect of the present invention will be described.

In the tire mold 2 according to the present invention, the cavity surface 16 for forming the tread surface is formed by arranging the pieces 12 side by side. A slit 20 is provided between the pieces 12 adjacent to each other. In the vulcanization step, the air between the low cover R and the cavity surface 16 moves to the slit 20 and is discharged from the slit 20.

As the mold is used, there are places where the width of the slit becomes smaller, which may reduce the exhaust performance. This can be a factor in tire bears. In this mold 2, the cavity surface 16 comprises an exhaust groove 22 extending along the boundaries of pieces 12 adjacent to each other. The opening 24 of the slit 20 is located on the inner surface of the exhaust groove 22. In this mold 2, air can move through the exhaust groove 22 even if a place where the width of the slit 20 becomes small occurs. In this mold 2, deterioration of exhaust performance due to a small slit 20 width is prevented. In this mold 2, the generation of bears is suppressed.

As the mold is used, there may be places where the width of the slit increases. The larger the width of the slit, the easier it is for the rubber composition to enter the slit. This can be a factor in the occurrence of burrs on the tire. In this mold 2, the opening 24 of the slit 20 is located on the inner surface of the exhaust groove 22. The exhaust groove 22 relieves the pressure at which the rubber composition enters the slit 20. The exhaust groove 22 prevents the rubber composition from entering the slit 20 even when the width of the slit 20 becomes large. With this tire, the generation of burrs is suppressed.

The exhaust groove 22 relaxes the force applied by the low cover R to the corner portion (opening 24 portion of the slit 20) of the piece 12 on the cavity surface 16 side. In this mold 2, the variation in the width of the slit 20 is reduced. In this mold 2, deterioration of exhaust performance due to a small width of the slit 20 is suppressed. In this mold 2, the penetration of the rubber composition into the slit 20 due to the increase in the width of the slit 20 is suppressed.

In the conventional mold, once the slit width fluctuates and bears and burrs start to occur on the tire, then bears and burrs are generated on the tire manufactured by this mold. It becomes difficult to continue using this mold. The mold needs to be replaced or adjusted. This affects tire productivity and manufacturing costs. As described above, in the present mold 2, even if the width of the slit 20 fluctuates, the generation of bares and burrs is suppressed. This mold 2 can be used for manufacturing tires for a long period of time. The mold 2 contributes to the improvement of productivity and the reduction of manufacturing cost.

In FIG. 6, the double-headed arrow Wg represents the width of the exhaust groove 22. This width Wg is measured at the opening of the exhaust groove 22 in a direction perpendicular to the extending direction of the exhaust groove 22. The width Wg is preferably 0.05 mm or more. By setting the width Wg to 0.05 mm or more, air can effectively move through the exhaust groove 22 even when the slit 20 width becomes small. From this viewpoint, the width Wg is more preferably 0.07 mm or more, and further preferably 0.09 mm or more. The width Wg is preferably 0.50 mm or less. By setting the width Wg to 0.50 mm or less, the ridges formed on the tire due to the rubber composition entering the exhaust groove 22 are inconspicuous. This tire has an excellent appearance. From this viewpoint, the width Wg is more preferably 0.45 mm or less, and further preferably 0.40 mm or less.

In FIG. 6, the double-headed arrow Dg represents the depth of the exhaust groove 22. This depth Dg is from the straight line connecting both ends of the opening of the exhaust groove 22 to the inner surface of the exhaust groove 22 when the opening 24 of the slit 20 is absent in the cross section perpendicular to the extending direction of the exhaust groove 22. It is defined as the maximum value of the distance.

The depth Dg is preferably 0.05 mm or more. By setting the depth Dg to 0.05 mm or more, air can effectively move through the exhaust groove 22 even when the width of the slit 20 becomes small. From this viewpoint, the depth Dg is more preferably 0.10 mm or more. The depth Dg is preferably 0.25 mm or less. By setting the depth Dg to 0.25 mm or less, the ridges formed on the tire due to the rubber composition entering the exhaust groove 22 are inconspicuous. This tire has an excellent appearance. From this viewpoint, the depth Dg is more preferably 0.20 mm or less.

As shown in FIG. 6, the contour of the cross section of the exhaust groove 22 is preferably an arc shape having an opening inside in the radial direction. By making the contour shape of the exhaust groove 22 in this way, air is effectively discharged through the exhaust groove 22. Further, the exhaust groove 22 having this shape is easy to form. The production of this mold 2 is easy.

In FIG. 6, the double-headed arrow Ws represents the width of the slit 20. This width Ws is measured in the opening 24 of the slit 20 in a direction perpendicular to the extending direction of the slit 20. The width Ws is preferably 0.02 mm or more. By setting the width Ws to 0.02 mm or more, air can effectively move through the slit 20. The width Ws is preferably 0.04 mm or less. It is difficult for the rubber composition to enter the slit 20 having a width Ws of 0.04 mm or less. In this tire, the generation of burrs due to the rubber composition entering the slit 20 is suppressed. This tire has an excellent appearance.

As described above, the cavity surface 16 preferably includes an exhaust groove 22 extending along the split position 26. The exhaust groove 22 provided at the split position 26 contributes to the exhaust of air. Further, by providing the exhaust groove 22 extending along the split position 26, the rubber composition can move to the exhaust groove 22 when the mold 2 into which the low cover R is inserted is closed. This prevents the rubber composition from being sandwiched between the segments 4 when the mold 2 is closed. This contributes to the exhaust of air. This contributes to the suppression of burrs.

As shown in FIG. 4, the boundary of the piece 12 is curved. In the mold 2 in which the boundary of the piece 12 is curved in this way, the force applied to the corner portion (the opening 24 portion of the slit 20) of the piece 12 on the cavity surface 16 side becomes non-uniform, and the width of the slit 20 fluctuates. Slits are likely to occur. The present invention is particularly effective for the mold 2 in which the boundary of the piece 12 is curved.

FIG. 7 shows a part of the tire mold 32 according to another embodiment of the present invention. This figure is a cross-sectional view showing the vicinity of the boundary of the piece 34 of the mold 32. The mold 32 is the same as the mold 2 of FIG. 1 except for the outline of the cross section of the exhaust groove 36. In this mold 32, the contour of the cross section of the exhaust groove 36 is a rectangular shape with an opening inside in the radial direction. In this mold, by making the contour shape of the exhaust groove 36 in this way, air is effectively discharged through the exhaust groove 36. Further, the exhaust groove 36 having this shape is easy to form. This mold is easy to make.

In the embodiment of FIG. 6, the contour of the cross section of the exhaust groove 22 is arcuate, and in the embodiment of FIG. 7, it is rectangular with an opening inside in the radial direction. Although not shown, the contour of the cross section of the exhaust groove may be trapezoidal with an opening inside in the radial direction. The contour of the cross section of the exhaust groove may be another polygon with an opening inside in the radial direction.

FIG. 8 shows a tire mold 42 according to still another embodiment of the present invention. This is a view of the segment 44 of the mold 42 as viewed from the inside in the radial direction. In FIG. 8, the direction indicated by the double-headed arrow A is the circumferential direction, the direction indicated by the arrow Y is the axial direction, and the direction perpendicular to the paper surface is the radial direction. This mold 42 is the same as the mold 2 of FIG. 1 except for the piece 46. In the segment 44 of the mold 42, a plurality of pieces 46 are arranged in parallel in the circumferential direction. The boundaries of the pieces 46 adjacent to each other are curved.

FIG. 9 is an enlarged view of the area M surrounded by the dotted line in FIG. As shown in the figure, a slit 48 is provided between the pieces 46 adjacent to each other. The slit 48 extends substantially the same width. The cavity surface 50 is provided with an exhaust groove 52 extending along the boundary of pieces 46 adjacent to each other. The opening 56 of the slit 48 is located on the inner surface of the exhaust groove 52.

FIG. 10 is a cross-sectional view taken along the line XX of FIG. In FIG. 10, the upper surface of the paper surface is the cavity surface 50. As shown in FIG. 8-10, in the mold 42, the cavity surface 50 is further provided with a groove (referred to as an auxiliary exhaust groove 54) extending so as to intersect or come into contact with the plurality of exhaust grooves 52. The sub-exhaust groove 54 connects a plurality of exhaust grooves 52. In the embodiment of FIG. 8, the sub-exhaust groove 54 extends linearly in the circumferential direction. The sub-exhaust groove 54 has an annular shape. The auxiliary exhaust groove 54 does not have to be annular. The sub-exhaust groove 54 may be interrupted by the exhaust groove 52. The sub-exhaust groove 54 may be interrupted between the exhaust groove 52 and another exhaust groove 52. The sub-exhaust groove 54 may extend at an angle with respect to the circumferential direction. The sub-exhaust groove 54 does not have to extend linearly. The sub-exhaust groove 54 may have a bend in the middle.

In this mold 42, the sub-exhaust groove 54 serves as an air movement path connecting a plurality of exhaust grooves 52 with which it contacts or intersects. Even if a slit 48 having a reduced width is generated, air can move not only in the exhaust groove 52 in which the opening of the slit 48 is located but also to another exhaust groove 52 through the sub-exhaust groove 54. .. This effectively contributes to the exhaust of air. In this mold 42, the generation of bears is suppressed more effectively.

In FIG. 10, the double-headed arrow Wb represents the width of the sub-exhaust groove 54. This width Wb is measured at the opening of the sub-exhaust groove 54 in a direction perpendicular to the extending direction of the sub-exhaust groove 54. The width Wb is preferably 0.05 mm or more. By setting the width Wb to 0.05 mm or more, air can effectively move through the sub-exhaust groove 54. From this viewpoint, the width Wb is more preferably 0.07 mm or more, and further preferably 0.09 mm or more. The width Wb is preferably 0.50 mm or less. By setting the width Wb to 0.50 mm or less, the ridges formed on the tire due to the rubber composition entering the sub-exhaust groove 54 are inconspicuous. This tire has an excellent appearance. From this viewpoint, the width Wb is more preferably 0.45 mm or less, and further preferably 0.40 mm or less.

In FIG. 10, the double-headed arrow Db represents the depth of the sub-exhaust groove 54. This depth Db is defined as the maximum value of the distance from the straight line connecting both ends of the opening of the sub-exhaust groove 54 to the inner surface of the sub-exhaust groove 54 in the cross section perpendicular to the extending direction of the sub-exhaust groove 54.

The depth Db is preferably 0.05 mm or more. By setting the depth Db to 0.05 mm or more, air can effectively move through the sub-exhaust groove 54. From this viewpoint, the depth Db is more preferably 0.10 mm or more. The depth Db is preferably 0.25 mm or less. By setting the depth Db to 0.25 mm or less, the ridges formed on the tire due to the rubber composition entering the sub-exhaust groove 54 are inconspicuous. This tire has an excellent appearance. From this viewpoint, the depth Db is more preferably 0.20 mm or less.

Hereinafter, the effects of the present invention will be clarified by Examples, but the present invention should not be construed in a limited manner based on the description of these Examples.

[Example]
The mold shown in FIG. 8 was manufactured. This mold has an exhaust groove and an auxiliary exhaust groove on the cavity surface. The specifications of the exhaust groove and the sub-exhaust groove are shown in Table 1. The outline of the cross section of the exhaust groove and the sub-exhaust groove is arcuate. This sub-exhaust groove has an annular shape extending in the circumferential direction. In this mold, the boundaries of the pieces are curved. The width Ws of the slit of this mold was 0.04 mm.

[Comparison example]
The mold of the comparative example was manufactured in the same manner as in the embodiment except that the cavity surface did not have the exhaust groove and the sub-exhaust groove.

[Continuous working days and production]
Tires were continuously produced with the molds of Examples and Comparative Examples. The number of days until bears and burrs that could not continue the production of tires and the number of tires produced so far were measured. This result is shown in Table 1 as an index with Comparative Example as 100. The larger the value, the more preferable. In the mold of the example, the evaluation was terminated when the number of days reached 2.8 times the production days of the mold of the comparative example. In fact, with the mold of the embodiment, it is possible to continue the production of the tire.

[Bear occurrence rate and burr occurrence rate]
For the tires produced by the above evaluation of the number of continuous working days and the number of production, the ratio of tires with bears and the ratio of tires with burrs were measured. Each result is shown in Table 1 as an index with Comparative Example as 100. The smaller the value, the more preferable.

As shown in Table 1, the mold of the example has a higher evaluation than the mold of the comparative example. From this evaluation result, the superiority of the present invention is clear.

The mold described above can be applied to the manufacture of various tires.

2, 32, 42 ... Mold 4, 44 ... Segment 6 ... Side plate 8 ... Bead ring 10 ... Holder 12, 34, 46 ... Piece 14 ... Piece inner surface 16 ... , 50 ... Cavity surface 18 ... Protrusions 20, 48 ... Slits 22, 36, 52 ... Exhaust grooves 24, 56 ... Slit openings 26 ... Split position 54 ... Sub Exhaust groove

Claims (7)

It has multiple pieces and
By arranging the above pieces, a cavity surface for forming the tread surface of the tire is formed.
A slit is provided between the above pieces adjacent to each other.
The cavity surface comprises an exhaust groove extending along the boundary of the pieces adjacent to each other.
The opening of the slit is located on the inner surface of the exhaust groove.
The cavity surface comprises an auxiliary exhaust groove that extends in contact with or intersects with the plurality of exhaust grooves and does not extend along any of the slits .
The width of the exhaust groove is 0.05 mm or more and 0.5 mm or less.
The depth of the exhaust groove is 0.05 mm or more and 0.25 mm or less.
A tire mold having a slit width of 0.02 mm or more and 0.04 mm or less . The tire mold according to claim 1 , wherein the contour of the cross section of the exhaust groove is rectangular or arcuate. The tire mold according to claim 1 or 2 , wherein the boundary between adjacent pieces is curved. The tire mold according to any one of claims 1 to 3 , wherein the sub-exhaust groove has an annular shape. The tire mold according to any one of claims 1 to 4 , wherein the width of the sub-exhaust groove is 0.05 mm or more and 0.50 mm or less. The tire mold according to any one of claims 1 to 5 , wherein the depth of the sub-exhaust groove is 0.05 mm or more and 0.25 mm or less. The process of obtaining a low cover,
And a plurality of pieces, a cavity surface for forming a tread surface of a tire is formed by arranging these pieces, a slit is provided between the pieces adjacent to each other, and the cavity surfaces are adjacent to each other. An exhaust groove extending along the piece is provided, an opening of the slit is located on the inner surface of the exhaust groove, and the cavity surface extends in contact with or intersects with a plurality of the exhaust grooves and extends along any of the slits. The sub-exhaust groove is provided , the width of the exhaust groove is 0.05 mm or more and 0.5 mm or less, the depth of the exhaust groove is 0.05 mm or more and 0.25 mm or less, and the width of the slit is A method for manufacturing a tire comprising a step of vulcanizing the low cover in a mold having a size of 0.02 mm or more and 0.04 mm or less .

Images